package com.leoman.helper.util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5Util {

    // 十六进制下数字到字符的映射数组
    private final static String[] hexDigits = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
            "a", "b", "c", "d", "e", "f" };

    /**
     * 对字符串进行MD5加密
     *
     * @throws NoSuchAlgorithmException
     */
    public static String encodeByMD5(String originString) {
        if (originString != null) {
            // 创建具有指定算法名称的信息摘要
            MessageDigest md = null;
            try {
                md = MessageDigest.getInstance("MD5");
            }
            catch (NoSuchAlgorithmException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            // 使用指定的字节数组对摘要进行最后更新，然后完成摘要计算
            byte[] results = md.digest(originString.getBytes());
            // 将得到的字节数组变成字符串返回
            String resultString = byteArrayToHexString(results);
            return resultString;
        }
        return null;
    }

    /**
     * 转换字节数组为十六进制字符串
     *
     * @param b
     *            字节数组
     * @return 十六进制字符串
     */
    private static String byteArrayToHexString(byte[] b) {
        StringBuffer resultSb = new StringBuffer();
        for (int i = 0; i < b.length; i++) {
            resultSb.append(byteToHexString(b[i]));
        }
        return resultSb.toString();
    }

    /** 将一个字节转化成十六进制形式的字符串 */
    private static String byteToHexString(byte b) {
        int n = b;
        if (n < 0)
            n = 256 + n;
        int d1 = n / 16;
        int d2 = n % 16;
        return hexDigits[d1] + hexDigits[d2];
    }

    public final static String getMessageDigest(byte[] buffer) {
        char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
                'e', 'f' };
        try {
            MessageDigest mdTemp = MessageDigest.getInstance("MD5");
            mdTemp.update(buffer);
            byte[] md = mdTemp.digest();
            int j = md.length;
            char str[] = new char[j * 2];
            int k = 0;
            for (int i = 0; i < j; i++) {
                byte byte0 = md[i];
                str[k++] = hexDigits[byte0 >>> 4 & 0xf];
                str[k++] = hexDigits[byte0 & 0xf];
            }
            return new String(str);
        }
        catch (Exception e) {
            return null;
        }
    }

}
